Transplant production system

ABSTRACT

A system for transplant production comprises: at least one air conditioner installed in a completely light shielding closed structure surrounded by a thermally insulated wall, for controlling temperature and humidity of air in the closed structure; at least one box-shaped culturing module disposed in an internal space of the closed structure, having a front face opening which is opened to the internal space of the closed structure; a plurality of transplant production shelves arranged vertically in a multi-layer in the culturing module to form a transplant production space between upper and lower transplant production shelves; a plurality of plug trays for holding a plant growing medium mounted on each transplant production shelf; a sub-irrigation unit capable of irrigation from a bottom of the plug trays mounted on each transplant production shelf; an artificial lighting unit provided on a back of each transplant production shelf for irradiating light to the lower plug trays; and at least one air fan fixed to a back wall of each transplant production shelf of the culturing module. By sucking air whose temperature and humidity have been controlled by the air conditioner using the air fan from the front face opening of the culturing module and sending the air to a rear of the back wall of each transplant production shelf, temperature-controlled and humidity-controlled air can be generated.

TECHNICAL FIELD

The present invention relates to a system for transplant production withmulti-layer shelving in a closed space. More specifically, the presentinvention relates to a transplant production system using an artificiallight source, an air conditioner and an automatic irrigation unit, andcapable of realizing a stable transplant production environment notinfluenced by an external environment and efficiently producinghigh-quality plug seedlings under a uniform growing condition.

BACKGROUND ART

Conventionally, as a method for growing seedlings of various plants,there is a transplant production method represented by a plant factory.This transplant production method is a method for stably growinghigh-quality uniform seedlings through labor-savings at a low cost byusing a closed-type transplant production system including an artificiallight source, air conditioner and an automatic irrigation unit tothereby artificially control light quantity, temperature, humidity, windspeed and irrigation quantity in a transplant production space tooptimum states.

As this type of closed-type transplant production system, an artificialenvironmental system is disclosed in Japanese Patent No. 3026253. Inthis system, an air conditioning chamber is formed inside of a ceilingwall of a box-shaped outer chamber constituted by a thermal insulatingmaterial, a blowing chamber and a suction chamber are formed inside ofopposed side walls of the outer chamber, respectively, and transplantproduction boxes are removably disposed in a multi-layer manner betweenthe blowing chamber and the suction chamber. Air in the system is blowninto a transplant production space from a honeycomb-structural wall ofthe blowing chamber and sucked by passing through a porous-plate wall ofthe suction chamber, and sent to the blowing chamber again by passingthrough a ventilation flue in the air conditioning chamber to therebycirculate the air. This circulation air is adjusted in terms oftemperature and humidity by an air conditioner and blower positioned inthe air conditioning chamber and circulated. However, in such a systemdescribed above, since the air conditioning chamber, the blowing chamberand the suction chamber are formed inside of the outer chamber, there isa problem in that utilization efficiency of transplant production spacein the outer chamber is deteriorated. Also, since special rectifyingstructure for uniformly blowing air from the blowing chamber is used,structure of the system becomes complex.

Moreover, as an automatic irrigation unit used for this type oftransplant production system, there is a unit disclosed by a reportentitled, “Development of an injection type sub-irrigation unit for plugtray”, presented in a joint meeting of three scientific societies,namely, The Society of Agricultural Meteorology of Japan, JapaneseSociety of Environment Control in Biology and Japanese Society of HighTechnology in Agriculture, in 1999. The automatic irrigation unitreported here injects proper amounts of water and a culture solution toa culture medium for a short time by inserting a plurality of nozzlesinto a plug tray from bottom holes thereof. This irrigation unit has afeature that excess water or excess culture solution is not dischargedbecause injected water does not leak from the bottom holes of the plugtray. It is necessary in such an irrigation unit, however, to prepare alarge number of nozzles to be inserted into all of the bottom holesformed on bottom walls of tens to hundreds of plugs for a single plugtray, mechanically insert these nozzles into all of the bottom holes,and then inject an equal amount of water from each of these nozzles.Thus, in order to realize these requirements, there is a defect in thata complex and expensive mechanism is required.

Further, as another automatic irrigation unit, there is a unit disclosedby a report entitled, “Simplification of an automatic irrigation unit onthe basis of evapotranspiration measurement of plug seedlingspopulation”, presented in a joint meeting of The Society of AgriculturalMeteorology of Japan and Japanese Society of Environment Control inBiology in 2000. In this automatic irrigation unit, an amount ofevapotranspiration of a plant body and a culture medium is measured as achange in seedling population weight for each plug tray by placing theplug tray on a pan balance, a switch contact point is set to a pointerof the balance, and the switch contact point directly detects movementof the pointer to designate start of irrigation to the seedlingpopulation. This unit has a feature in that irrigation using a properamount of water can be conducted without discharging excess water, sinceirrigation is started on the basis of the amount of evapotranspirationand irrigation using a minimum necessary amount of water being performedby using a subtimer. However, this report reveals that, since operationof the pointer has a mechanical resistance and movement of the pointeris directly influenced by gravity, operation of the pointer isincomplete or operational accuracy thereof has a problem.

Furthermore, Japanese Patent Laid-Open Specification No. 2001-346450discloses a sub-irrigation unit, i.e. a watering unit capable ofwatering from a bottom of a plug tray, for use in a transplantproduction system with multi-layer shelving in a closed space. Thissub-irrigation unit is provided with a shallow quadrangular box havingthree sides surrounded by side walls and having a bottom wall face. Adrainage groove is formed at a side of the box having no side wall. Awater supply pipe is disposed on a side wall face of the side of the boxopposed to the drainage groove. A porous sheet of a synthetic resin isput on a bottom wall face of the box and plug trays are mounted on theporous sheet. According to the sub-irrigation unit having theabove-described structure, water supplied from the water supply pipe isabsorbed by the porous sheet due to its capillary action and spreadsentirely to the bottom wall face of the box in a short time to therebyattain a water pool state at a predetermined water level and uniformlysupply water to culture media contained in respective plugs from plugholes formed at a bottom of the respective plugs arrayed in the plugtray due to a capillary phenomenon. Since the culture medium in eachplug comes into a water saturated state in a short time due to thecapillary phenomenon, it is not necessary to maintain the pool state fora long time. However, unless a pump having a large discharge quantity isused, water does not spread to the bottom wall face of the box in itsentirety and therefore a pool state is not realized. After irrigation isstopped, water remaining in the porous sheet is discharged to thedrainage groove from an end of the porous sheet hanging down into thedrainage groove. However, since the bottom of each plug contacts theporous sheet even after irrigation is stopped, the vicinity of the plughole is easy to maintain in a wet state. As a result, roots of seedlingsextend to outside from the plug hole, and therefore a problem occurs ina removal operation of seedlings from the plugs, and there is a dangerof damaging the roots. To prevent the roots of seedlings from extendingup to the vicinity of the plug hole by drying the vicinity of the plughole after irrigation is stopped, it is proposed to form a plurality ofsmall protrusions on the plug bottom so that the plug bottom does notdirectly contact with the porous sheet. However, a satisfied dry stateis not always obtained.

SUMMARY OF THE INVENTION

In view of the above circumstances, the inventors of the presentinvention have eagerly studied in order to overcome the above-describedproblems present in the technical field of culturing seedlings using aclosed-type transplant production system and provide a transplantproduction technique capable of efficiently producing uniform andhigh-quality seedlings at a low energy and a low cost. The presentinvention has been accomplished as a result of such studies.

The following are objects of the present invention:

(1) To provide a closed-type transplant production system having a highspace utilization rate in a closed space;

(2) To provide an energy-saving transplant production system capable ofefficiently circulating air in a closed space by a simple structurewithout using complex rectifying structure, and capable of realizingeffective temperature and humidity control by minimum necessary power;and

(3) To provide a transplant production system having a sub-irrigationunit requiring only minimum necessary irrigation to culture seedlingsand capable of effectively drying a bottom of plug trays when irrigationis stopped.

A transplant production system according to the present inventioncomprises:

at least one air conditioner installed in a completely light shieldingclosed structure surrounded by a thermally insulated wall, forcontrolling temperature and humidity of air in the closed structure;

at least one box-shaped culturing module disposed in an internal spaceof the closed structure, having a front face opening which is opened tothe internal space of the closed structure;

a plurality of transplant production shelves arranged vertically in amulti-layer manner in the culturing module to form a transplantproduction space between upper and lower transplant production shelves;

a plurality of plug trays for holding a plant growing medium mounted oneach transplant production shelf;

a sub-irrigation unit capable of irrigation from a bottom of the plugtrays mounted on each transplant production shelf;

an artificial lighting unit provided on a back of each transplantproduction shelf, for irradiating light to the lower plug trays; and

at least one air fan fixed to a back wall of each transplant productionshelf of the culturing module,

whereby air whose temperature and humidity have been controlled by theair conditioner is sucked by the air fan from the front face opening ofthe culturing module and sent to the rear of the back wall of eachtransplant production shelf to circulate the air in the closedstructure.

It is also possible that a plurality of culturing modules are disposedin the internal space of the closed structure so that they are arrangedin one line with their front face openings facing in the same direction.

Alternatively, it is possible that a plurality of culturing modules arearranged in two lines with their front face openings in the same linefacing in the same direction, and the front face openings in one lineare opposed to the front face openings in the other line, and a workspace and concurrently an air circulation path are formed between thetwo lines of the culturing modules.

The sub-irrigation unit mounted on each transplant production shelf ispreferably provided with a shallow quadrangular box-shaped irrigationtray having three sides surrounded by side walls and having a bottomwall face, a water supply pipe for supplying water into the irrigationtray is disposed in the irrigation tray, a drainage groove joined to thebottom wall face is formed at a side of the irrigation tray having noside wall, with the drainage groove and the bottom wall face beingpartitioned by a dam, and structure for maintaining a gap between thebottom wall face of the irrigation tray and a bottom of the plug tray ata time of mounting the plug tray on the bottom wall face of theirrigation tray is provided on the bottom wall face of the irrigationtray.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view showing an example of a transplantproduction system of the present invention.

FIG. 2 is a schematic longitudinal sectional view showing a flow of airin an internal space of the transplant production system shown in FIG.1.

FIG. 3 is a front view showing an example of a culturing module used forthe transplant production system of the present invention.

FIG. 4 is a side view of the culturing module shown in FIG. 3.

FIG. 5 is a plan view showing an example of a sub-irrigation unit usedfor the transplant production system of the present invention.

FIG. 6 is a perspective view of the sub-irrigation unit shown in FIG. 5.

FIG. 7 is a schematic longitudinal sectional view along line X-X in FIG.5.

FIG. 8 is a schematic longitudinal sectional view showing anotherexample of the sub-irrigation unit used for the transplant productionsystem of the present invention.

FIG. 9 is a schematic plan view showing another example of thetransplant production system of the present invention.

FIG. 10 is a schematic plan view showing still another example of thetransplant production system of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferable example of a transplant production system of the presentinvention is described below by referring to an example shown in FIGS. 1and 2. A transplant production system of the present invention is aclosed-type transplant production system constituted by arranging aplurality of box-shaped culturing modules 3, 4, 5, and 6 (four in thecase of this illustrated example) in an internal space of a completelylight shielding closed structure 1 surrounded by a thermally insulatedwall. In the present invention, the closed structure denotes a structurehaving an internal space closed by being surrounded by a wall forcutting off external air temperature and natural light. A typicalstructure is a box-shaped hexahedron obtained by combining reinforcingbars, slates and a thermal insulating material. An external shape of thestructure is not restricted to a boxy shape. It is allowed to use abarrel shape, hemi-cylindrical shape or hemispherical shape.

A size of an internal space of the closed structure 1 may be determinedto proper dimensions depending upon a number of culturing modules to bearranged in the internal space. In the case of the example shown in FIG.1, two culturing modules 3 and 4 are arranged in one line with theirfront face openings facing in the same direction. In addition, twoculturing modules 5 and 6 are also arranged in one line with their frontface openings facing in the same direction. These two lines of theculturing modules are disposed in the internal space of the closedstructure 1 so that the front face openings in one line are opposite tothe front face openings in another line. Moreover, a work space in whichone or more workers can work is formed between these two lines of theculturing modules. In order to improve an area utilization rate andspace utilization rate of the internal space of the closed structure 1,it is preferable to form the work space as small and narrow as possible.When the culturing modules 3 to 6 are displaced in the closed structure1, a path of air passing through the culturing modules is formed byproviding a space having a width of about 50 to 300 mm between an insidewall face of the closed structure and backs of the culturing modules.

Concerning internal dimensions of the closed structure 1 in the exampleshown in FIGS. 1 and 2, a width is 3,400 mm, a depth is 2,500 mm, and aheight is 2,200 mm. Providing an air curtain inside of a hinged door 2of an entrance is preferable because it is possible to prevent outsideair from coming in when a worker passes through the door 2.

The closed structure 1 is provided with an air conditioner having afunction for controlling temperature and humidity of air in the internalspace and circulating air whose temperature and humidity have beencontrolled to predetermined conditions. Indoor units 7, 8, 9, and 10 ofthe air conditioner are fixed to an upper portion of the inner face ofthe closed structure side wall and an outdoor unit (not illustrated) ispositioned to the outside of the closed structure 1. One air conditionermay control the temperature and humidity of the internal space in itsentirety depending on the size of the closed structure. However, inorder that temperature-controlled and humidity-controlled air iseffectively circulated in the internal space of the closed structure 1,it is preferable to use a plurality of indoor units of the airconditioner corresponding to the number of the culturing modules, andfix each indoor unit to the upper portion of the inner face of theclosed structure side wall located at the rear of the back wall of eachculturing module.

As shown in FIGS. 3 and 4, the culturing module 3 disposed in theinternal space of the closed structure 1 is provided with a boxy outershape having side walls 3 a and a back wall 3 b formed on side and backfaces thereof, respectively, and having a front face opening. In theculturing module 3, a plurality of culturing shelves 12 are verticallyarranged in a multi-layer at certain intervals, whereby area utilizationefficiency of the transplant production space is improved. It ispreferable that a height of each culturing module 3 is set to about2,000 mm at which a worker can work, a width of each transplantproduction shelf 12 is set to, for example, about 1,000 to 2,000 mm atwhich a plurality of plug trays of synthetic resin each having tens tohundreds of plugs (small pots) arrayed in a grid pattern can be mountedand a temperature and humidity in each shelf can be controlled at aconstant value, and a depth of each transplant production shelf 12 isset to 500 to 1,000 mm. Concerning external dimensions of the culturingmodule 3 of the illustrated example, a height is 1,650 mm, a width is1,300 mm, and a depth is 650 mm and four plug trays 40 (refer to FIG. 1)are mounted on each transplant production shelf 12. Concerningdimensions of one plug tray, a width is about 300 mm and a length isabout 600 mm in general.

Transplant production shelves 12 arranged in the multi-layer in theculturing module 3 (four stages in the example shown in FIG. 3) arealmost horizontal and a transplant production space is formed betweenthe transplant production shelves 12. The transplant production shelflocated at a lowest-stage is mounted on a pedestal 3 c of the culturingmodule and horizontality of the transplant production shelves 12 can beadjusted by an adjuster 3 d set on the pedestal. By decreasing aninterval between adjacent transplant production shelves and increasing anumber of transplant production shelves, it is possible to improve aspace utilization rate. However, when the interval between the adjacenttransplant production shelves is too small, there are disadvantages inthat operability for removing or inserting plug trays is deterioratedand a maximum length of seedlings cannot be secured. Therefore, it ispreferable that the interval is set to about at least 300 mm. Thetransplant production shelves 12 are formed preferably by using metallicplates, a metallic net, and metallic bars.

On each of the transplant production shelves 12 are mounted asub-irrigation unit to be described herein later and a plurality of plugtrays. Further, an artificial lighting unit 13 is provided on a back ofeach transplant production shelf 12 to irradiate light to plants grownin the plug trays of the transplant production shelf just below thelighting unit 13. In the case of the transplant production shelf locatedat a highest-stage, the artificial lighting unit 13 is provided on aback of the top wall 3 e of the culturing module.

A fluorescent lamp is preferable as a light source of the artificiallighting unit 13. It is possible to properly select candlepower andlength of the fluorescent lamp in accordance with the width and lengthof the transplant production shelf 12 and the interval between adjacenttransplant production shelves 12. For example, when a transplantproduction shelf having a width of 1,200 mm and a length of 600 mm isused and the interval between adjacent transplant production shelves is350 mm, it is possible to attach four to eight fluorescent lamps, eachof which has a length of 1,200 mm and a candlepower of 32 to 45 W, inparallel on the back of each transplant production shelf.

As shown in FIG. 3, a plurality of air fans 15 are fixed to back wall 3b of each stage of the transplant production shelves 12. By operatingthe air fans 15, it is possible to generate air circulation flows shownby arrows in FIG. 2 in the internal space of the closed structure 1.That is, the air whose temperature and humidity have been controlled byindoor units 7 to 10 of the air conditioner is sucked into thetransplant production space of each stage of the transplant productionshelves 12 from the front face opening of each of the culturing modules3 to 6, and discharged to the rear of the back wall of each culturingmodule. The air discharged to the rear of the back wall of eachculturing module is sucked into the indoor units 7 to 10 of the airconditioner, and, after the temperature and humidity of the air havebeen controlled, blown out to the front face openings of the culturingmodules 3 to 6. When two lines of the culturing modules 3 and 4 and theculturing modules 5 and 6 are arranged so that the work space is formedbetween them as in the example shown in FIGS. 1 and 2, the work spacefunctions concurrently as an air circulation path. Therefore, it ispossible to provide an effective circulation flow.

When the circulation flow passes through the transplant productionshelves 12 of the culturing modules 3 to 6, the circulation flow isaccompanied by water vapor evaporated from irrigation units, culturemedia and plant seedlings, and also by heat discharged from theartificial lighting units 13. By controlling the temperature andhumidity of the circulation flow using the indoor units 7 to 10 of theair conditioner and continuously circulating the flow, it is possible tokeep the internal space of the closed structure 1 at a temperature andhumidity environment optimum for plant growth.

When the width of each transplant production shelf 12 is small, one airfan 15 may be fixed to the back wall 3 b of each stage of the transplantproduction shelves. However, such a layout is not preferable because ofoccurrence of uneven ventilation when a large width of the transplantproduction shelf 12 is used. As shown in FIG. 3, by disposing aplurality of air fans 15 in each stage of the transplant productionshelf 12 (one air fan is disposed for each of four plug trays; total offour air fans in the example shown in FIGS. 1 and 3), it becomespossible to eliminate uneven ventilation, and uniform ventilation anduniform air circulation are realized. When a plurality of air fans aredisposed, it is allowed that air suction force per one air fan iscomparatively small.

A sub-irrigation unit is mounted on each of the transplant productionshelves 12 arranged in the multi-layer in the culturing modules 3 to 6and employs a system in which irrigation is performed from a bottom ofthe plug trays mounted on each transplant production shelf. An exampleof the sub-irrigation unit is shown by a top view in FIG. 5, aperspective view in FIG. 6, and a sectional view in FIG. 7. Thisillustrated sub-irrigation unit 30 is provided with a shallowquadrangular box-shaped irrigation tray 31 having three sides surroundedby side walls 31 a, 31 b and 31 c and a bottom wall face 31 d. Adrainage groove 32 joined to the bottom wall face 31 d is formed at aside of the irrigation tray 31 having no side wall, and a drainage port32 a is formed at one end of the drainage groove 32. Further, a watersupply pipe 33 for supplying water (a culture solution containingfertilizer) into the irrigation tray 31 is also disposed. The watersupply pipe 33 may be disposed in any position as long as water can besupplied into the irrigation tray 31 from that position. In the case ofthe illustrated example, the water supply pipe 33 is disposed on theside wall 31 a of the irrigation tray opposite to the drainage groove 32and water is supplied from a plurality of small holes 33 a formed in thewater supply pipe. Moreover, the drainage groove 32 and the bottom wallface 31 d are partitioned by a dam 34 and a cutout 34 a is formed on apart (both ends in the case of the illustrated example) of the dam 34.

The sub-irrigation unit used in the present invention is characterizedin that structure for maintaining a gap between the bottom wall face ofthe irrigation tray and the bottom of the plug tray is provided. The gapis maintained at a time of mounting the plug tray on the bottom wallface of the irrigation tray. In the example shown in FIGS. 5 to 7, thisgap holding structure is constituted by a plurality of ribs 35 formed onthe bottom wall face 31 d of the irrigation tray. The ribs 35 extend inparallel with each other toward the drainage groove 32, and the plugtrays 40 are mounted on these ribs 35.

It is allowed that the irrigation tray 31 is made of a metal orsynthetic resin, a width and thickness of the irrigation tray 31 aresubstantially the same as those of the transplant production shelf 12arranged in each stage in the culturing modules 3 to 6, and a depth isset to about 30 to 50 mm. In the example of the illustratedsub-irrigation unit 30, dimensions are such that drainage grooves 32protrude from the front face openings of the culturing modules at thetime of mounting the irrigation trays 31 on the transplant productionshelves of the culturing modules 3 to 6 (refer to reference numeral 32in FIG. 4). By protruding the drainage groove 32 from the front faceopening of its culturing module, water discharged from the drainage port32 a of the drainage groove 32 of the irrigation tray 31 mounted on eachstage of the transplant production shelves 12 is easily collected anddrained to outside of the closed structure 1.

When a predetermined quantity of water is continuously supplied from thesmall holes 33 a formed in the water supply pipe 33 of thesub-irrigation unit 30, the water is spread over the bottom wall face 31d of the irrigation tray and stopped by the dam 34 to thereby accumulateup to a predetermined water level and form a water pool state. Whilewater is supplied from the water supply pipe 33, water leaks little bylittle from the cutouts 34 a (width of about 10 mm, for example) formedin the dam 34 into the drainage groove 32. However, by adjusting asupplied water quantity and a water quantity leaking from the cutouts,the pool state having a water level of about 10 to 12 mm can bemaintained in the irrigation tray 31. In this case, by narrowing a widthof the cutouts to decrease outflow of the water, the supplied waterquantity can be decreased and a small water supply pump may be used.When the pool state having such a water level as described above ismaintained, water is soaked up, due to capillary action, to culturemedia in plugs 41 from plug holes 42 formed on bottoms of the plugs 41arrayed in the plug tray 40 mounted on the ribs 35 (average height ofabout 7 mm, for example), and thus the culture media in all of the plugs41 come into a water saturated state in a short time. In addition, sincethe culture media in all of the plugs 41 arrayed in the plug tray 40come into the water saturated state uniformly, it is unnecessary tocontinue irrigation anymore. Thus, it is possible to apply uniformirrigation to all the plugs 41 of the plug tray 40 mounted on each stageof the transplant production shelves without accurately equalizing thewater quantity supplied to each stage of the transplant productionshelves 12.

When supply of water from the water supply pipe 33 is continued evenafter culture media in all the plugs of the plug tray come into thewater saturated state, excess water is drained into the drainage groove32. After automatically stopping the supply of water, although most ofthe water in the irrigation tray 31 is drained in a short time to thedrainage groove 32 through the cutouts 34 a formed in the dam 34, somewater remains on the bottom wall face 31 d of the irrigation tray toproduce a wet state. However, since the bottom of the plug tray 40 israised from the bottom wall face 31 d of the irrigation tray by virtueof the ribs 35, a gap is maintained between the bottom of the plug tray40 and the bottom wall face 31 d of the irrigation tray. By flowing thetemperature-controlled and humidity-controlled air through the gap, thevicinity of the plug holes 42 is made to come into a dry state in ashort time.

When the vicinity of the plug holes 42 formed at the bottom of the plugtray 40 is kept in a wet state, roots of seedlings easily extend towardthe water. However, when the vicinity of the plug holes 42 is kept in adry state, roots of seedlings do not extend to this location in the drystate. This phenomenon is referred to as an air pruning effect anddenotes a state in which roots are pruned by using an air layer as aboundary. According to the example of the sub-irrigation unit 30 asshown in FIGS. 5 to 7 used for the transplant production system of thepresent invention, it is possible to securely bring the vicinity of theplug holes 42 into a dry state in a short time and positively generatethe air pruning effect. As a result, it is possible to prevent roots ofseedlings from extending outside from the plug holes 42. Therefore, at atime of fix planting of produced seedlings, a removal operation from theplugs 41 of seedlings becomes easy and roots are not damaged.

In the case of the example of the illustrated sub-irrigation unit 30, asshown by the sectional view in FIG. 7, the bottom wall face 31 d of theirrigation tray 31 is tilted in a direction toward the drainage groove32. Thereby, it is possible to drain water to the drainage groove 32 ina short time when irrigation is stopped. Moreover, in the case where thebottom wall face 31 d is tilted, it is preferable to change heights ofthe ribs 35 so that top surfaces 35 a of the ribs become horizontal,such that the plug tray 40 mounted on the ribs can be kept horizontal.

FIG. 8 shows another example of the sub-irrigation unit used for thepresent invention. For omitting description, members same as those inFIGS. 5 to 7 are designated by the same numerals. In sub-irrigation unit30′ as shown in FIG. 8, when plug tray 40 is mounted on bottom wall face31 d of an irrigation tray, a lower tray 50 is intervened between thebottom wall face 31 d of the irrigation tray and the plug tray 40. Thelower tray 50 has a rigidity capable of supporting the plug tray 40having plugs 41 containing culture media, and is provided with aplurality of small holes 51 formed on a bottom wall thereof and aplurality of protrusions 52 attached to a back face thereof. Theseprotrusions 52 function as structure for maintaining a gap between thebottom wall face 31 d of the irrigation tray and the bottom of the plugtray 40 when the plug tray 40 is housed in the irrigation tray togetherwith the lower tray 50.

Also in the sub-irrigation unit 30′ as shown in FIG. 8, when a waterpool state having a predetermined water level is realized by supplyingwater from water supply pipe 33, water is introduced into the lower tray50 from the small holes 51 of the lower tray 50 and water is soaked upto culture media in the plugs 41 from plug holes 42 formed in bottoms ofthe plugs 41 of the plug tray 40 through capillary action. Afterstopping supply of water from the water supply pipe 33, excess water isdrained to drainage groove 32, and a small amount of water remains onthe bottom wall face 31 d of the irrigation tray. Even if the bottomwall face 31 d is in a wet state, the gap is maintained between thebottom of the plug tray 40 and the bottom wall face 31 d of theirrigation tray by the protrusions 52 on the back face of the lower tray50, and temperature-controlled and humidity-controlled air flows throughthe gap to thereby make the vicinity of plug holes 42 a dry state in ashort time.

Also in the case of the example in FIG. 8, it is possible, similarly tothe case of the example in FIGS. 5 to 7, to drain water to the drainagegroove 32 in a short time when irrigation is stopped, by tilting thebottom wall face 31 d of the irrigation tray in a direction toward thedrainage groove 32.

The plug tray 40 mounted on the irrigation tray 31 of the sub-irrigationunits 30 and 30′ mounted on each stage of the transplant productionshelves 12 is formed by arraying tens to hundreds of plugs 41 in a gridpattern and integrating them into a tray shape. A width of one plug trayis 300 mm and its length is about 600 mm, and various types of plugtrays are commercially available. In general, the plug tray ismanufactured from a synthetic resin sheet by a forming method utilizingdifferential pressure. As a shape of the plug 41, an invertedfrustoconical shape is preferably employed and either of a circular coneor pyramid may be used. It is preferable to use a plug having a depth ofapproximately 15 to 50 mm and a capacity of approximately 4 to 30 ml,and having a plug hole 42 in its bottom and capable of irrigation fromthe bottom.

In the case of the example of the transplant production system of thepresent invention shown in FIGS. 1 and 2, two lines for a total of fourculturing modules 3 to 6, that is, a line of two culturing modules 3 and4 and a line of two culturing modules 5 and 6, are arranged in theinternal space of the closed structure 1 so that the front face openingsin one line are opposed to the front face openings in the other line.Since the transplant production system of the present invention has astructure in which culturing modules are arranged in the internal spaceof the closed structure, it is possible to freely construct a transplantproduction system corresponding to a scale by properly selecting a sizeof the closed structure and a number of culturing modules to be arrangedin the closed structure. For example, FIG. 9 shows an example in whichtwo culturing modules 3 and 4 are disposed in an internal space ofclosed structure 1 so that they are arranged with their front faceopenings facing the same direction. Further, FIG. 10 shows an example inwhich one culturing module 3 is disposed in an internal space of smallclosed structure 1. In FIGS. 9 and 10, the members same as those inFIGS. 1 and 2 are designated by the same numerals for omitting theirdescription.

In the transplant production system of the present invention, it is notalways necessary to fix the indoor units 7 to 10 of the air conditionerinstalled in the closed structure 1 to the upper portion of the innerface of the side wall of the closed structure 1 located at the rear ofthe back wall of the culturing modules 3 to 6. The indoor units may befixed to any position as long as an air circulation flow can begenerated in the internal space of the closed structure by virtue of theindoor units of the air conditioner and the air fans 15 fixed to theback wall of the culturing modules. For example, as shown by the examplein FIG. 10, it is also possible to fix indoor unit 7 of the airconditioner to an inner face of a side wall of the closed structure 1opposite to the front face opening of the culturing module 3.

Since the internal space of the closed structure is highly airtight, ina case where a normal ventilation condition is applied, it is necessaryto artificially supply carbon dioxide gas consumed throughphotosynthesis during culturing of seedlings. Therefore, as shown inFIG. 1, a liquid carbon dioxide cylinder 16 is positioned outside of theclosed structure 1 and a carbon dioxide analyzer (not illustrated) ispositioned inside of the closed structure. It is possible to maintaincarbon dioxide concentration in the internal space at a predeterminedvalue by a system for discharging a necessary amount of carbon dioxidefrom the carbon dioxide cylinder 16 to the internal space of the closedstructure in accordance with a signal sent from the carbon dioxideanalyzer, when the carbon dioxide concentration in the internal space ofthe closed structure measured by the carbon dioxide analyzer becomes nomore than a certain value.

By culturing seedlings in the internal space of the closed structureusing the transplant production system of the present invention, it ispossible to automatically control environmental conditions such asquantity of light, temperature, humidity, carbon dioxide and waterpreferable to culture seedlings. In addition, since all the seedlings oneach of the transplant production shelves in the culturing modules withmulti-layer shelving can be cultured under the same environment, it ispossible to improve uniformity of obtained seedling quality. Theseedling quality here denotes external features such as length ofhypocotyl, diameter of hypocotyl, leaf color, leaf area and the like,and quality features such as a forming position of a floral bud,presence or absence of bolting and the like.

INDUSTRIAL APPLICABILITY

According to the present invention described above, the followingadvantages can be obtained.

(1) By virtue of the indoor units of the air conditioner installed inthe internal space of the closed structure and the air fans fixed to theback walls of the culturing modules, it is possible to effectivelygenerate a circulation flow of temperature-controlled andhumidity-controlled air in the internal space. Therefore, installationof complex rectifying structure is not required and efficient control oftemperature and humidity in the closed space can be performed withminimum necessary power. As a result, it is possible to provide anenergy-saving and low-cost transplant production system.

(2) A circulation flow of temperature-controlled and humidity-controlledair can effectively be generated by a simple configuration in which theindoor units of the air conditioner and the air fans are disposed in theinternal space of the closed structure. Therefore, since it isunnecessary to form an air conditioning chamber, a blowing chamber, asuction chamber and the like in the internal space, a wide space forculturing seedlings can be provided and as a result, the spaceutilization rate can be improved.

(3) By using the sub-irrigation unit having the dam formed on the bottomwall face of the irrigation tray, a water pool state having apredetermined water level can be easily realized. Thus, since culturemedia in all plugs of the plug tray can be brought into a watersaturated state in a short time by soaking up water from the bottom ofthe plugs, an amount of necessary irrigation can be minimum.

(4) By using the sub-irrigation unit provided with the gap holdingstructure between the bottom wall face of the irrigation tray and thebottom of the plug tray, a gap can be maintained between the bottom ofthe plug tray and the bottom wall face of the irrigation tray at thetime of stopping irrigation and the vicinity of the plug holes can bebrought into a dry state by circulating temperature-controlled andhumidity-controlled air through the gap. As a result, it is possible toprevent roots of seedlings from extending from the plug holes to outsideand simplify an operation for removing a seedling from the plug.

1. A system for transplant production, comprising: a light shieldingclosed structure including a surrounding thermally insulated wall; anair conditioner in said closed structure for controlling temperature andhumidity of air in said closed structure; a box-shaped culturing module,having a front face opening, within said closed structure; transplantproduction shelves arranged vertically in said culturing module; a plugtray, for holding a plant growing medium, on each of said shelves; asub-irrigation unit, capable of providing irrigation from a bottom of acorresponding said plug tray, on said each of said shelves, saidsub-irrigation unit including (i) a shallow quadrangular box-shapedirrigation tray having three sides surrounded by side walls and having abottom wall face, (ii) a water supply pipe within said irrigation trayfor supplying water into said irrigation tray, (iii) a drainage groovejoined to said bottom wall face at a side of said irrigation tray havingno side wall, (iv) a dam partitioning said drainage groove and saidbottom wall face, and (v) structure on said bottom wall face formaintaining a gap between said bottom wall face and a bottom of saidcorresponding said plug tray at a time of mounting said correspondingsaid plug tray on said bottom wall face; an artificial lighting unit,for irradiating light from above to said corresponding said plug tray,associated with said each of said shelves; and a fan, associated withsaid each of said shelves, for sucking air, the temperature and humidityof which have been controlled by said air conditioner, from said frontface opening of said culturing module and conveying the air toward arear end of said culturing module so as to circulate the air within saidclosed structure.
 2. The system according to claim 1, furthercomprising: another air conditioner in said closed structure forcontrolling temperature and humidity of air in said closed structure;another box-shaped culturing module, having another front face opening,within said closed structure; additional transplant production shelvesarranged vertically in said another culturing module; another plug tray,for holding a plant growing medium, on each of said additional shelves;another sub-irrigation unit, capable of providing irrigation from abottom of a corresponding said another plug tray, on said each of saidadditional shelves; another artificial lighting unit, for irradiatinglight from above to said corresponding said another plug tray,associated with said each of said additional shelves; and another fan,associated with said each of said additional shelves, for sucking air,the temperature and humidity of which have been controlled by saidanother air conditioner, from said front face opening of said anotherculturing module and conveying this air toward a rear end of saidanother culturing module so as to circulate this air within said closedstructure.
 3. The system according to claim 2, wherein said airconditioner is fixed to an upper portion of a wall of said closedstructure at the rear end of said culturing module, and said another airconditioner is fixed to an upper portion of a wall of said closedstructure at the rear end of said another culturing module.
 4. Thesystem according to claim 3, wherein said fan is at a rear portion ofsaid each of said shelves and is generally beneath said air conditioner,and said another fan is at a rear portion of said each of saidadditional shelves and is generally beneath said another airconditioner.
 5. The system according to claim 4, wherein said wall towhich said air conditioner is fixed is spaced from the rear end of saidculturing module by a distance within a range of from about 50 mm to 300mm, and said wall to which said another air conditioner is fixed isspaced from the rear end of said another culturing module by a distancewithin a range of from about 50 mm to 300 mm.
 6. The system according toclaim 3, wherein said wall to which said air conditioner is fixed isspaced from the rear end of said culturing module by a distance within arange of from about 50 mm to 300 mm, and said wall to which said anotherair conditioner is fixed is spaced from the rear end of said anotherculturing module by a distance within a range of from about 50 mm to 300mm.
 7. The system according to claim 2, wherein the rear end of saidculturing module is spaced from a wall of said closed structure by adistance within a range of from about 50 mm to 300 mm, and the rear endof said another culturing module is spaced from a wall of said closedstructure by a distance within a range of from about 50 mm to 300 mm. 8.The system according to claim 1, wherein said air conditioner is fixedto an upper portion of a wall of said closed structure at the rear ofsaid culturing module.
 9. The system according to claim 8, wherein saidfan is at a rear portion of said each of said shelves and is generallybeneath said air conditioner.
 10. The system according to claim 9,wherein said wall to which said air conditioner is fixed is spaced fromthe rear end of said culturing module by a distance within a range offrom about 50 mm to 300 mm.
 11. The system according to claim 8, whereinsaid wall to which said air conditioner is fixed is spaced from the rearend of said culturing module by a distance within a range of from about50 mm to 300 mm.
 12. The system according to claim 1, wherein saidstructure for maintaining a gap between said bottom wall face and thebottom of said corresponding said plug tray comprises ribs extending onsaid bottom wall face in a direction from said water supply pipe to saiddrainage groove.
 13. The system according to claim 1, wherein saidstructure for maintaining a gap between said bottom wall face and thebottom of said corresponding said plug tray comprises protrusions formedon a back surface of a perforated lower tray positioned between saidbottom wall face and said corresponding said plug tray.
 14. The systemaccording to claim 1, wherein said dam defines at least one cutout. 15.The system according to claim 1, wherein said bottom wall face isinclined in a direction away from said drainage groove.
 16. The systemaccording to claim 1, further comprising: another box-shaped culturingmodule, having another front face opening, within said closed structure;additional transplant production shelves arranged vertically in saidanother culturing module; another plug tray, for holding a plant growingmedium, on each of said additional shelves; another sub-irrigation unit,capable of providing irrigation from a bottom of a corresponding saidanother plug tray, on said each of said additional shelves; anotherartificial lighting unit, for irradiating light from above to saidcorresponding said another plug tray, associated with said each of saidadditional shelves; and another fan, associated with said each of saidadditional shelves, for sucking air, temperature and humidity of whichhave been controlled, from said front face opening of said anotherculturing module and conveying this air toward a rear of said anotherculturing module so as to circulate this air within said closedstructure, wherein said culturing module and said another culturingmodule are linearly arranged with said front face opening and saidanother front face opening facing in the same direction.
 17. The systemaccording to claim 1, further comprising: another box-shaped culturingmodule, having another front face opening, within said closed structure;additional transplant production shelves arranged vertically in saidanother culturing module; another plug tray, for holding a plant growingmedium, on each of said additional shelves; another sub-irrigation unit,capable of providing irrigation from a bottom of a corresponding saidanother plug tray, on said each of said additional shelves; anotherartificial lighting unit, for irradiating light from above to saidcorresponding said another plug tray, associated with said each of saidadditional shelves; and another fan, associated with said each of saidadditional shelves, for sucking air, temperature and humidity of whichhave been controlled, from said front face opening of said anotherculturing module and conveying this air toward a rear of said anotherculturing module so as to circulate this air within said closedstructure, wherein said culturing module and said another culturingmodule are arranged such that said front face opening and said anotherfront face opening oppose one another so as to define a work space andan air circulation path therebetween.
 18. The system according to claim1, further comprising: a carbon dioxide analyzer within said closedstructure; and a carbon dioxide cylinder outside said closed structurefor supplying a predetermined amount of carbon dioxide into said closedstructure in accordance with an electrical signal sent from said carbondioxide analyzer.
 19. The system according to claim 1, wherein the rearend of said culturing module is spaced from a wall of said closedstructure by a distance within a range of from about 50 mm to 300 mm.